1. Technical Field
Example embodiments of the present invention relate in general to a method of scanning an access point and more specifically to a method of scanning an access point using an active scanning method in a wireless local area network (WLAN) system.
2. Related Art
Various wireless communication techniques are being developed along with the recent development of an information communication technology. In particular, wireless local area network (WLAN) is a technology that can provide a wireless connection to the Internet in a limited service area such as a home or office building using portable terminals, for example, a personal digital assistant (PDA), a laptop computer, and a portable multimedia player (PMP) based on a wireless frequency technology.
Standards for WLAN technology is developed and standardized by IEEE 802.11 working group (WG) in the Institute of Electrical and Electronics Engineering (IEEE) 802.11. IEEE 802.11a provides a transfer rate of 54 Mbps using 5 GHz unlicensed band. IEEE 802.11b provides a transfer rate of 11 Mbps by using direct sequence spread spectrum (DSSS) in 2.4 GHz band. IEEE 802.11g provides a transfer rate of 54 Mbps by using orthogonal frequency division multiplexing (OFDM) in 2.4 GHz band. IEEE 802.11n provides a transfer rate of 300 Mbps for two spatial streams by using multiple-input multiple-output OFDM (MIMO-OFDM). IEEE 802.11n supports a channel bandwidth of up to 40 MHz and, in this case, provides a transfer rate of 600 Mbps.
Along with the wide deployment of WLAN and the diversification of applications using WLAN, new WLAN techniques are increasingly needed to support higher throughput than IEEE 802.11n. Very high throughput (VHT) WLAN is one of IEEE 802.11 WLAN techniques, which is proposed to support a data processing rate of 1 Gbps or more. In particular, IEEE 802.11ac is developed as a standard for providing a very high throughput on the 5 GHz band, and IEEE 802.11ad is developed as a standard for providing a very high throughput on the 60 GHz band.
In a system based on the WLAN techniques, a method of scanning an access point includes an active scanning method and a passive scanning method.
In the active scanning method for the access point, a terminal (station) transmits a probe request frame to an access point, and upon receiving the probe request frame, the access point responds by transmitting a probe response frame to the terminal. Generally, the probe response frame includes much information and thus occupies a wireless channel for a long time.
In an environment in which there are a plurality of access points and a plurality of terminals, the respective probe request frames of the plurality of terminals cause a considerable number of probe response frames, which competitively occupy a wireless channels. Thus, terminals may not receive a probe response frame from a desired access point in a short time and should stay awake while receiving a probe response frame from an even undesired access point in order to receive the desired probe response frame.
In addition, since the terminal does not know a channel in which the desired access point is present, the terminal should sequentially perform the access point scan process for each channel. In this case, the terminal moves to another channel after sufficiently waiting until the terminal receives the probe response frame of the desired access point.
That is, in the active scanning method for the access point, it takes a long time to receive the probe response frame of the desired access point.